History of the Atlantic Cable & Undersea Communications
from the first submarine cable of 1850 to the worldwide fiber optic network

TAT-1 Fault Repair, July 1959

Introduction: The 1956 opening of the first transatlantic telephone cable system, TAT-1, marked the beginning of the modern era of cable communications. While the cable itself worked flawlessly for its entire design life, it was not immune to the external hazards which dated back to the very beginnings of the cable industry in 1850. This article describes the repair of damage to TAT-1 caused by an unidentified fishing trawler in July 1959.

Thanks to the Museum of Communication in Burntisland, Fife, Scotland, for providing the documentation on which this article is based.

--Bill Burns

The Cable Failure

At 1822 EDT on Thursday, July 23, 1959, the West-East direction of the New York-Montreal-London Transatlantic System failed without warning. The failure was indicated by loss of all pilots and abnormal power feed voltage and current readings in the deep sea cable section between Oban, Scotland and Clarenville, Newfoundland.

TAT-1 route map
The fault was very close to the east end of the cable at Oban

At the time, maintenance of the Oban-Clarenville section of TAT-1 was the responsibility of the Long Lines Department of AT&T. The Bell Telephone Laboratories, British Post Office, Canadian Overseas Telecommunication Corporation and Eastern Telephone and Telegraph Company participated in various phases of the repair and investigation of this occurrence.

Repair Operations

Prearranged restoration procedures for such an occurrence were put into action immediately. Only two regularly operated radio circuits from White Plains to London were commercial at the time of the failure, but within two hours other radio equipments were quickly pressed into service to establish a total of 12 radio circuits to London. Full service was restored at 0540 EDT on July 24 by using the Clarenville-Penmarch West-East cable of TAT-2, which had recently been completed but was not yet in regular use, and extending the circuits to London on three carrier groups routed via Paris.

Measurements were made using the Fault Localization Test Set (FLTS) by the Oban and Clarenville cable stations and the data were reviewed. The measurements made from Oban located the fault 8 NM west of the second repeater (Repeater 50) or about 62 NM from the Scottish terminal station. A low-resistance fault was indicated.

After power was turned down on the cable, extinguishing the gas tubes, Oban turned up power and measured repeater crystal noise peaks. They were able to measure the peaks from two repeaters only, which verified the measurements made with the FLTS that the trouble was between the second and third repeaters from Oban. In the course of the repair, the actual fault was found at 61.17 NM from Oban.

Detail of TAT-1 cable route off the Scottish coast

As the break was in shallow water, it was determined that the the cable ship Iris (owned and operated by the British Post Office) would be adequate for the repair. Fortunately the Iris was docked at her home base at Dalmuir, Scotland, and after raising steam and loading cable repeaters and test equipment, the Iris left port at 0844 EDT Saturday, July 25.

It was estimated that it would take about 16 hours for the ship to reach the location of the cable break. During the travel time of the ship further measurements were made at Clarenville and Oban to verify the initial data and make every possible refinement in their interpretation.

Since the trouble was suspected to be caused by trawler activity, arrangements were made to have two RAF planes scout the area of the measured location at daybreak; however, poor weather conditions delayed the take-off for several hours. The planes covered an area of about 150 miles radius, photographing all shipping or fishing activities they saw. The result of this survey was not conclusive.

The Iris arrived at a point about 8.6 NM west of Repeater 50 at 0023 EDT on July 26 and proceeded to grapple for the cable and pick it up. On being brought aboard the cable parted and it was necessary to make another pickup slightly to the west of the original point.

At Pickup Point 2 the cable tested clear to Clarenville and the end was buoyed off. The ship then moved to Pickup Point 3 and recovered the cable ends west and east of this point until the cable break was located. This proved to be 6.94 NM west of Repeater 50 or 61.17 NM west of Oban, in 52 fathoms of water. The cable at this point was A type.

The ship then proceeded east to Pickup Point 4, tested clear to Oban, and at 1010 EDT began to make a splice to the A cable aboard ship. This splice was completed at 1600 EDT and the cable was laid westward to the buoyed end of the cable. After reaching the buoy, the west splice was started at 1815 EDT and was completed and overboard at 2215 EDT on July 26.

Initial power was applied to the cable at 2300 EDT and action was normal. At 2345 EDT the pilots were tested through from Clarenville to Oban and other transmission tests were made. No change in the overall transmission characteristics was noted.

 The cable was repaired and completely returned to service at 0135 EDT on July 27, 1959, a total elapsed time of slightly over three days.

Condition of Recovered Cable

The cable which was recovered between the two splice points was in generally good condition except for one section, 1.50 NM west of the cable break. This piece of cable showed evidence of trawler damage, signs of having been under tension and was in generally poor condition.

Cable break: West end

Cable break: East end


The repair of the cable was completed in remarkably short time. The following are some of the significant conclusions that should be noted:

  1. From the information at hand it is believed that the break was caused by an unidentified trawler whose gear snagged the cable. Since the cable parted under tension, it is assumed that it was never brought to the surface by the trawler but parted due to heavy strain being applied approximately at right angles to the cable. 

  2. Advance planning for the repair operation was good and contributed heavily to the speed of the repair. The fact that a suitable ship was available at the cable and repeater storage point at Dalmuir, Scotland was a large contributing factor.

  3. A competent, experienced crew aboard the Iris expedited repairs. The travel time for the ship to the break was small (about 16 hours) and the fault was in shallow water (about 52 fathoms). All these factors contributed to a speedy restoration.

  4. The measured location of the fault was good and again proved the accuracy of the FLTS (Fault Localization Test Set) as compared to DC resistance measurements.

  5. The weather conditions were good throughout the repair operation which considerably expedited its completion.

  6. Repeater operation has shown no evidence of damage due to the transients produced when the cable was shorted at a high-voltage point. Transmission and crystal measurements on the repaired cable indicated substantially no change from the last routine tests made before the break occurred.

Last revised: 11 March, 2023

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